Method and apparatus for suppression of antiaircraft fire

ABSTRACT

An aerial weapon is provided for the suppression of antiaircraft artillery fire against an air attack. This concept has been called various names in the past, notably AFIRM standing for Anti-Flak InfraRed Missile. A first rocket delivers the missile which descends on a parachute until the heat of an antiaircraft gun is sensed. A second rocket propels the missile to target under control of heat sensing guidance and control unit.

Elite States atent m1 Swarm [4 1 Apr. 17, 1973 METHOD AND APPTUS FORSUPPRESSION OF ANTHAIRCa L i FIRE Inventor:

Edwin G. Swann, China Lake, Calif.

The United States of America as represented by the Secretary of the NavyFiled: Mar. 5, 1970 Appl. No.: 22,101

Assignee:

Primary Examiner-Samuel Feinberg AltorneyR. S. Sciascia, Roy Miller andGerald F. Baker [57] ABSTRACT An aerial weapon is provided for thesuppression of antiaircraft artillery fire against an air attack. Thisconcept has been called various names in the past, notably AFlRMstanding for Anti-Flak InfraRed Missile. A first rocket delivers themissile which descends on a parachute until the heat of an antiaircraftgun is sensed. A second rocket propels the missile to target undercontrol of heat sensing guidance and control unit.

4 Claims, 8 Drawing Figures PATENTEDAPR 1 mm 3,727. as 1 SHEET 1 [IF 3FIGQl EDWIN G. SWANN INVENTOR.

ROY MILLER ATTORNEY GERALD E BAKER AGENT PATENTED 1 H975 3. 727. 86 lSHEET 3 [1F 3 METHOD AND APPARATUS FOR SUPPRESSION OF ANTIAIRCRAFT FIREBACKGROUND OF THE INVENTION:

Air attack during prolonged conflict has encoun tered increasingresistance from ground defenses. Such ground defenses include rapid fireguns ranging from machine guns to heavy artillery generally employingvarious types of fire control systems. The guns are disposed in an areato be defended in accordance with a doctrine of employment which may bedetectable after the fact but which may well be very difficult topredict should the enemy find it desirable to conceal his tactics.Alternatives that are available to the enemy, for example, are: (a)disposition close in or dispersed on the approaches to a target area;(b) concealment of gun sites with heavy camouflage or nonconcealmentcoupled with construction of decoy sites; (c) use of barrage fire asopposed to the use of tracking fire. The effective employment ofantiaircraft artillery and light guns has three distinct but relatedeffects on the attack. Some aircraft are hit and suffer damage ordestruction. To avoid the first effect, or to ameliorate it, theattackers deliver their weapons from greater distances thus reducingaccuracy and effectiveness. Finally, in attempting to stay out of rangeof artillery, the attacking aircraft are caused to fly into thedetection and launch envelopes of surface to air missile systems.

The objective of flak suppression is to significantly reduce theeffectiveness of antiaircraft artillery and light guns. The most directway of achieving this objective is to destroy enemy gun systems bydirect attack. It is operationally difficult to apply this approachbecause it involves the destruction of a very large umber of relativelyinvulnerable targets, and because it places the primary target ofinterest second in the sequence of attacks. Furthermore, it more thanever would lead to a demand for a specially designed weapon to overcomethe invulnerability of the targets and to aid in reducing thevulnerability of the aircraft while making such attacks. Finally, itplays into the hands of the enemy whose objective in the employment ofantiaircraft artillery is to reduce he effectiveness of air attacks onhis primary targets. A less direct way to achieve the objective of flaksuppression is to deter he enemy from the use of his guns during theperiods when our attack aircraft are most vulnerable, that period whenthey are approaching and delivering on the primary target. Deterrence ofthis sort can be achieved if there is a threat of direct retaliationtriggered by the undesired action. In other words, if the attackingaircraft can present a threat to the gun systems that they will beattacked, if and when they open fire during some limited period of time,then some measure of suppression will be achieved. This is the nature ofthe method that is described in this invention.

SUMMARY OF THE INVENTION Light guns and artillery that have been evolvedthrough a long history for the purpose of shooting at airplanes havecertain characteristics that are readily distinguished. First, they areguns, generally of high muzzle velocity. When in use they radiate largequantities of energy of acoustic and electromagnetic nature resultingfrom imperfect conversion of the stored chemical energy of thepropellant to kinetic energy of 0 sound pulses. These are shortlyfollowed by nearly omnidirectional radiation in the infrared from themuzzle, barrel, breech parts and expended ammunition cases. Typicallythis radiation becomes significant after 10 to 20 round of rapid fireindependently of the calibre of the gun. This general behavior stemsfrom the fact that the heat capacity of the gun is roughly directlyrelated to the amount of energy that is expended in each firing. Thethermal lag for the elevated temperatures to reach the outer surfaces ofthe gun parts is nearly exactly compensated for by the loWer rates offire of large guns over small guns. Some early exploration of thefeasibility of detecting guns by their infrared radiation has beenaccomplished. This primarily was accomplished in tests conducted asRandsburg Wash Test Range of the Naval Weapons Center. The concept thatis described herein depends on the above inherent characteristics ofantiaircraft artillery.

According to the invention a flak suppression aircraft launchesparachute missiles toward flak sites that cover the primary target andthe egress route from it. Even if the flak sites are undetectable,approach and egress corridors can be seeded with these missiles. Aplurality of weapons are suspended over the flak sites on their deployedparachutes. When the following strike aircraft run in on the target,opening fire from the guns is detected acoustically by the missile, thedirection to the strongest source is detected and the infrared seeker ofthe detecting missile is trained in that direction. A small angle searchis performed by the seeker until a lock-on is obtained. When lock-on isacquired by the infrared seeker, he second rocket is initiated and themissile separated from its parachute. The missile then homes on thesource of the infrared radiation and, even if the gun ceases fire, themissile is still able to home on the energy that continues to beradiated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. I is a planview, partly in section of a preferred embodiment of a weapon useable inthe disclosed system;

FIG. 2 is a plan view of the weapon of FIG. 1 in a first stage ofdeployment;

FIG. 3 is a sketch depicting terrain in a typical area;

FIG. 4 is a sketch depicting a closer view of the area of FIG. 3;

FIGS. 5 and 6 are sketches depicting yet closer view of the area;

FIG. 7 is a view similar to FIG. 2 showing a deployed weapon suspendedby parachute; and

FIG. 8 is a view similar to FIG. 7 just after release of the weapon.

DESCRIPTION OF THE INVENTION Av missile according to a preferredembodiment of the invention, is shown at in FIG. 1. The missile 10 hastwo rocket motors 12, 14. The first (12) is the larger of the two andserves to emplace the missile. Even with this rocket 12 the missile is arelatively low velocity projectile. Approximately 15 pounds of solidpropellant (18) gives it a boost velocity over the launch aircraftvelocity of about 500 feet per second. The missile 10 is launched on anupward trajectory (see FIG. 4) to give it an altitude gain of a fewthousand feet at a point 2 to 4 miles from the launch point. As themissile begins the downward part of its trajectory a barometric sensor22 separates the first rocket motor 12 and deploys the parachute 24. Theparachute 24 is designed to provide a descent rate of 25 to 50 feet persecond. While falling, the missile listens for gunfire from an area thatis covered by a cone of about 45 degrees half angle below it.

The missile listening referred to is based on the use of acousticdefection of gun fire to locate targets. This is accomplished by fouracoustic detectors (see FIG. 2) that are mounted on folding arms 32.During missile flight these detector arms 32 are folded along the skin16 of the missile and lie in recessed grooves 34. When the missile 10 issuspended from its parachute 24 its acoustic detector arms 32 areunfolded or hinged forward forming quadrature pairs. Direction of thesound arrival is determined by arrival time differences in each of thetwo quadrature planes. The location direction thus determined for soundpulses is used to slave the infrared seeker 20 in a limited area search.With a 4 foot base line and maximum desired look angles of 45 degrees,time differences of the order of zero to 3 milliseconds will bemeasured. It should be possible to measure the arrival time differencesin the very quiet environment of a parachute fall with an accuracy ofplus or minus 0.25 milliseconds. If this can be achieved a search of aconical angle of 5 degrees will be adequate for the infrared seeker. Togive added discrimination against background noise and spurious signalsan integration of five to ten pulses will be required for the slaving ofthe seeker. In this way the seeker will not be slaved to search fortargets that are not likely to radiate sufficiently in the infrared toserve as good targets.

The second rocket motor 14 of the missile is ignited upon defection andlock-on by the infrared seeker 20. It separates the parachute 24 andpropels the missile 10 toward the target. This rocket 14 is relativelylow performance having about 10 pounds of propellant 28 to provide themissile with a velocity of about 400 feet per second. The missilewarhead 26 weighs about 50 pounds and is designed primarily forpersonnel kill and secondarily for gun damage.

Missile Characteristics Length, in. Diameter, in. 6 Fin span, in. 18Acoustic span, in. 48 Total weight lb. 200 Warhead weight, lb. 50 lstrocket prop., lb. 15 2nd rocket prop., lb. 10 Launch range, n. mi. 2 to4 Launch altitude, k ft. 2 to 15 Operating alt., k ft. 15 to 3 Parachuterate, ft/sec 25 to 50 Acoustic look angle degrees 45 IR Seeker range, n.mi. 4 Possible cost, 5000.00

What is claimed is: 1. A weapons system comprising: a plurality ofmissiles;

means for deploying said missiles over a selected area; said means fordeploying including hover means maintaining said missiles over said areafor a finite period of time; gunfire detection means on said missilesaffected by the sound of gunfire in said area to produce a signaloutput; said detection means including means responsive to said signal,or separating said missile from said hover means; guidance means in saidmissiles affected by an aspect of a gun installation and effective tocause said missile when separated from said hover means to home on a guninstallation site in said area. 2. A weapons system according to claim 1wherein said hover means comprises a parachute.

3. A weapons system according to claim 2 wherein said guidance meanscomprises heat sensitive means.

4. A weapons system according to claim 1 wherein said guidance meansincludes heat sensitive means.

1. A weapons system comprising: a plurality of missiles; means fordeploying said missiles over a selected area; said means for deployingincluding hover means maintaining said missiles over said area for afinite period of time; gunfire detection means on said missiles affectedby the sound of gunfire in said area to produce a signal output; saiddetection means including means responsive to said signal, forseparating said missile from said hover means; guidance means in saidmissiles affected by an aspect of a gun installation and effective tocause said missile when separated from said hover means to home on a guninstallation site in said area.
 2. A weapons system according to claim 1wherein said hover means comprises a parachute.
 3. A weapons systemaccording to claim 2 wherein said guidance means comprises heatsensitive means.
 4. A weapons system according to claim 1 wherein saidguidance means includes heat sensitive means.